The sputtering method is a type of physical vapor deposition techniques, in which glow discharge is generated with an electrode attached with film material (target) as a cathode in a vacuum container with inert gas such as Ar being introduced thereinto, so that ions generated in the discharge collide against the cathode with an energy of several hundreds of electron volts corresponding to the discharge voltage to form film on a substrate by deposition of particles released as a reaction of the collision. The film forming process is used as a practical film forming process, which can generate even more intense glow discharge with a magnetron sputtering method in which a magnetic field is applied near the surface of the target.
A problem sometimes pointed in such a sputtering method is that the formed film is not dense enough due to small energy of particles depositing on substrates.
In glow discharge in general sputtering, ionized target particles (sputtering particles) are small in number, but if sputtering particles can be ionized somehow, dense film could be obtained. Ionized sputtering particles are given energy to head to the substrate side by a negative bias applied to substrates on which film is formed (objects to be processed) or a substrate holder for holding the substrates. The energy will act for densification such as to increase film bonding strength, providing dense film as a result.
Various methods have been proposed to solve the problem, one of which is the proposed technology that generates discharge for film forming in a pulsed manner with very high power density.
For example, Patent Document 1 proposed for magnetron sputtering that DC pulses be applied to the target so as to form substantially uniform plasma by applying pulses with negative voltages with sharp rising edges to the target and causing the gas in front of the target to be fully ionized very rapidly. The document disclosed a specific pulse condition as a favorable condition, which is 0.1 kW to 1 MW for the power during pulsing; 50 μs to 1 ms, more preferably 50 to 200 μs, most preferably 100 μs for the pulse width; 10 ms to 1000 s, preferably 10 to 50 ms for the pulse intervals; and 0.5 to 5 kV for the pulse voltage.
The inventor of the Patent Document 1, Kouznetsov, reported in a Non-Patent Document 1 that an experiment of film forming was carried out with a peak power of 100 to 500 kW (equivalent to a target power density of 0.6 to 2.8 kW/cm2), an Ar pressure of 0.06 to 5 Pa, a pulse width of 50˜100 us and a repetition frequency of 50 Hz, and that, as a result, the ion current was as high as 1 A/cm2 on a substrate of film forming and the evaporated target vapor was ionized at about 70%. Due to a high ratio of ionization of vapor used for film forming, it is expected to obtain high adhesiveness between the film and the substrate as well as possibly dense film formation.
Patent Document 2 disclosed that a target material such as chromium was sputtered by adding a power of 1 kW/cm2 or more to the target, and that the sputtered sputtering particles were ionized to be used for pre-treatment of substrates.
Patent Document 3 proposed an opposing target sputter device and disclosed that ionization was recognized with sputtering particles sputtered with a maximum volume power density of 83 W/cm3 or more, which is obtained from the DC power supplied to the targets divided by the volume of the region enclosed by opposing targets. In this case, the distance between the opposing targets was 1 cm, the area of a target was 12 cm2 (2 cm×6 cm), and the total target area was 24 cm2. This corresponds to a power density of 41.5 W/cm2 when converted to a power density per target area.
Summering up these conventional technologies of Patent Documents 1 to 3 and Non-Patent Document 1, it is understood that providing a target with a power of 41.5 W/cm2 or more in power density is useful for process utilizing ionization of a target material (ionization of sputtering particles), which ionization may not be otherwise obtained in general sputtering, but the power differs depending on the forms of cathodes. It is understood that providing a power of 0.6 kW/cm2 or more in power density to a target becomes useful process in the planer magnetron sputtering method.
In the above-mentioned high-power pulse sputtering method that supply DC high-power pulses to the target (high-power pulse sputtering), however, the target material is ionized in a large quantity and the ionized target particles (sputtering particles) are electrically charged positively, which will be recovered by the target having a negative potential, resulting in reduction of the film forming rate corresponding thereto.
Patent Document 4 disclosed a device that solves the problem of the reduction of film forming rate. The device disclosed in Patent Document 4 comprises a DC power source, a DC pulse power source comprising a pulse circuit and a DC power source, a pair of a cathode and an anode, wherein the device supplies, between the cathode and the anode, high-power DC pulse power for a high-power pulse sputtering method to be superimposed on DC power for a general DC sputtering method. The device is adapted to secure a film forming rate to objects to be processed by continuously supplying the DC power to the cathode, where a target is loaded, as well as to form dense film by ionizing sputtering particles sputtered during the application of the DC pulse power intermittently superimposed on the DC power.
In the case of a sputter device in which a sputter evaporation source, i.e., the electrode where a target is loaded, is supplied with continuous DC power and intermittent high-power DC pulse power to be superimposed thereon, an extremely high-power DC pulse power source is required so that high-power DC pulse power such as of a power density of 0.6 kW/cm2 to 2.8 kW/cm2, for example, can be supplied to the sputter evaporation source having a large size, where a target is loaded, when making film formation onto objects to be processed having a large film forming area. Therefore, considering production in a large quantity, it would be technically difficult to obtain such a DC pulse power source.
On the other hand, in order to achieve production in a large quantity, if a plurality of sputter evaporation sources are disposed and DC pulse power sources are each provided to each of the sputter evaporation sources for film formation onto objects to be processed having a large film forming area, each output of the DC pulse power sources could be reduced. This, however, has a disadvantage that a DC pulse power source is required to each of the sputter evaporation sources, as a result, the sputter device becomes expensive.